Method of laying out gears



April 3, 1929. H. D. CROFT METHOD OF LAYING OUT GEARS Filed Match 29,1928 v INVENTOR.

ATTORNEY.

Patented Apr. 23, 1929.

warren STATES PATENT OFFICE.

D. CROFT, OF SPRINGFIELD, MASSACHUSETTS, ASSIGNOR TO PERKINSMA- HIE/AMCHINE AND GEAR COMPAN PORATION OF MASSACHUSETTS.

My invention relates to methods Y, 011 VTEST SPRINGFIELD, MASSACHUSETTS,A COR- METHOD OF LAYING OUT GEARS.

Application filed March 29, 1928. Serial No. 265,746.

improv of laying out bevel gears t ements in or cutting as those of thebreaching or milling type; and the primary object is to enable bevelgears by the single-cut pr closely approximate by a great saving resultserated te to be those having eth, where in time, labor, and expense.

This method 0t laying out a b which gear may be of any any number ofteeth, is sim put into laying out the stance and as size produced ocess,which gears very true genevel gear, and have ple and can be practicewithout the exercise of a great amount of skill beyond that required inmy method.

obtain be vel gears the teeth of ly approximate generated teeth as suchgears useful for a great many with greater or less su I obtain tormlysatisfactory,

Other in the course of t generated tooth in the first ina first orpreliminary step in are various methods of bevel gears having true salways more entails large expense, and e from time to time to which socloseto render purposes,

ccess. Vith my method results which are dependable, uniobjects andadvantages w and highly eliicient.

ill appear he following description.

I attain the objects and secure the advantages of my invention in themanner in detail The accompanying drr-rwings, in. which lilie mesh in gamples ot the in the laying on gears being smaller tha fore termed apinion; Fig.

cal view ing the in same; Fig. 3, a diagrammatlcal view section of thegear illustr '1- laying out grainmati c tions of front, or

below.

l 'ence characters designate l are supplied t the method,

bevel gears oi? a section 0:!

the teeth thereof;

said gear and pinion at toe ends of the teeth, she

said teeth, when laid out accordi described il-ze parts through twointerucrete or;

ota

ating the method of Fig. al view of the intermeshing seci, a diatheinner, wing how mg to the and pinions of any size or sizes, and havingany numbers 01 teeth.

In the first view, the inside back angle line is represented at 3-3, theoutside back-angle line at 4+4, the cutting-angle line at 5-5, theface-angle line at 6-6, and the cone-am gle line at 7+7. The cone-angleline 7 is common to both the pinion 1 and the gear 2,

while each tooth of each of these members has a cutting-angle line 5 anda face-angle line 6, and they do not pass through the cone apex,indicated at S, of said members, but those of the pinion and those ofthe gear cross and pass on opposite sides of said apex. T he pinioncutting-angle and face-angle lines and the gear cutting angle andface-angle lines also cross the cone-angle'line 7. Naturallythere are ormay be cases where the :l'ace angles of a gear and pinion, either orboth, are other than those herein shown.

In Figs. 2 and 3, the theoretical generated tooth lines are dotted,while the reconstructed tooth lines, forsinglecut teeth. which are theobjective of the new layout, are in full. I

The pitch circles at the toe and heel ends of the pinion teetl'i arerespectively represented at 9-9 and 101() the pitch circles at the toeand heel ends of the gem.- teeth are respectively represented at 1111and 12-12 in Fig. 3.

Although the width of a tooth and the width of the space between twoadjacent teeth on any pitch circle are usually the same or equal, thereare, of course, cases wherethey are not the same or equal. applied tothe tooth spaces.

At 13-13 arerepresented curves which form the outline at the toe end or"a theoretically. perfect, generated tooth slot, and at 1313 arerepresented curves which form the outline at the heel end of said slot,in the pinion 1, Fig. 2. Similarly, in Fig. 3, the curves, at the toeend of a theoretically perfect, generated tooth slot in the gear 2',

in Fig. 2, and

The lay-out is '151o at the too.

are represented at 14l-]/l, and the curves at the heel end of said slotare represented at l l'-l l'.

Prin'iarily to the first step in the method, or perhaps thetheoretically perfect generatedoutlincs the toe and heel ends of a toothor of a tooth slot in the bevel gear or pinion to be out, with asingle-cut tool, are laid out in the usual manner, or a K101'(lll1g tothe customary rules, as at 18 and 13, rcs} )ectively, for the pinion 1,and at 1 1 and. 14, respectively, for the gear 2; The outlines 13 and 13and I l and l t here a re in \olute curves, but such outlines might becycloidal or other curves, or appro1-tin'iations of any or all of thesame. Next, two comparatively small, outline cicles, 1515 are foundwhich approxiniate the tooth-forming portions of the involute curves 13,applied so that said circles pass through the points on the pitch circle9 of the pinion through which the involute curves 13 pass. From theaforesaid points on the pitch circle to the full depth of the toothslot, or to the total-depth circle represented at 1616, the includedportions of the small circles 15 outline a tooth, or, as has beenexplained, adjacent sides of two adjacent teeth, from said pitch circleto said full depth, and said small circles also outline the said sidesbeyond or outside of said pitch circle. Similarly two comparativelysmall circles 17 are applied at the toe end of a tooth slot in the gear2, and portions of said circles outline the sides of said slot from thepitch circle 11 to the total-depth circle represented at 1818 in Fig. 3.This full or total depth in each case is the same for both the generatedand the approximated conditions, and said total depth is instrumental indetern'iining the cutting angle ot the single-cut tooth, which angle isdetermined by a line connecting the total depth of the tooth slot at thetoe end with the low point or total depthv t said slot at the heelendsee 5 in Fig. 1.

To determine the form of the tooth oi the pinion at the heel end, twosmall, outline circles, as 19, each of which is of the same diameter asthat 0t either circle 15, and the distance between centers of thecircles in both pairs is the same, or in any event, the distance betweencenters of the circles 19 is never less than the distance betweencenters or? the :ircles 15, are located over the involute curves 13 sothat they intersect the pitch circle at the points where said pitchcircle is in rsected by said involute curves, and said out no circlesare connected by an are of a circle parallel or concentric with thepitch circle, and having the same relation to a line connect 'ng thecenters of said outline circles as does the total depth circle to a lineconnc ng the centers of the outline circles Thus is determined thetotal-depth circle 20-20 at the heel end,

it better be termed the first step,

i c i rcie cutting angle is which necessarily is deeper than thetotaldepth circle at the heel end of the involute teeth, as is clearlyshown in Fig. 2, because the distance upward from line connecting thecenters or the circles 1919 to the pitch sn1all, outline circles 21which correspond in size with the circles 17, and the centers of whichare in no case nearer together than are the centers of the circles 17,in a similar manner to that just described relative to the pinion teeth,whereby the dedenduin at the heel of the tooth is found and atotal-depth l 23-23 established. 7

A line or plane extending between the total-depth circles at the toe andheel of any tooth slot detern'iines the cutting angle. This usuallydillerent from the angle of the generatedtooth itis usually necessary incutaccepted cutting condition, and

ting to tip either the blank or the cutting tool,

or both, more than under ating conditions; there might be cases,however, where the tipping of either or both inen'ibers would be lessthan under generating conditions.

In cutting any bevel gear in accordance with my lay out therefor, thecutting portion ol the tool is shaped in crows section to conform to theshape of the tooth slot at the toe end in the lay-out, and said tool andthe blank to be cut are set relatively so that the tool conforms to thecutting angle. Due to this formation and angular positioning of thetool, said tool cuts and sinks deeper at the heel end of the slot thanit does at the toe end. This is necessary because the width ot' thespace at the heel end or" the slot is greater (wider) than that 01 thespace at the toe end 0t said slot, and the tool. must cut throughbetween the points on the pitch circle which represent the width thereonof the space lJG-' tween the teeth at the heel end, as well as throughbetween the points on the pitchcircle which represent the width thereonoi the space between the teeth at the toe end. i

The face angle 6-43 of the tooth determined by a line drawn from thehigh point on. the outside diameter of the toe to the high point on theoutside diameter of the heel.

The centers of the outline circles 15 and 19 of the pinion 1 are oncircles 2l-24t and 25-25, respectively, which latter circles areconcentric with the pitch circles 9 and 10 and the total-depth circles16 and 2t); and the centers of the outline circles 17 and 21 ot the gear2 are on circles 26-2G and 27-27, respectively, which latter circles areconcentric With the pitch circles 11 and 12 and the total depth circles18 and 23.

. tooth slot, in approximating "erated tooth slot at the toe lines atthe toe end Although I have described above theusual and generallypreferred manner of putting mymethod into effect and use, it isconceivable that some departure in matters of detail, in addition tothose hereinbeiore intimated, necessary because of some special orunusual condition or conditions, may be made without violating thespirit of the invention or exceeding the scope of what is claimed.

I claim:

1. A method of laying out single-cut bevel gears consisting in layingdown the pitch circles at the toe and heel ends, and the totaldepthcircle at the toe end, of a developed the developedcurve outlines withcircles which pass through the pitch circle at the toe end, and inapplying similar circles at the heel end in a manner to cause them topass through the normal points of intersection between the sides of theslot and the pitch circles at that end, said total-depth circle at thetoe end being constant, but the total-depth circle at the heel end,because its are between the sides of the slot is approximately equal tothe arc of the total-depth circle that is between said sides, g

at the toe end, being deeper than the normal total-depth circle at saidheel end.

2. A method of laying out single-cut bevel gears consisting inestablishing pitch circles and determining the generated outlines of adeveloped tooth slot at the toe and heel ends, and establishing thetotal-depth circle at the toe end, in approximating with circles theinVol-ute outlinesat the toe end, which latter circles pass through thepoints of intersection between said outlines and the pitch circle at theend, and in applying similar outline circles at the heel end in a mannerto cause them to pass through the normal points of intersection betweensaid outlines and the pitch circle at that end.

3. The method of laying out single-cut bevel gears consisting in layingout a genand heel ends, in approximating the generated-curve outwithcircles, which outline circles pass through the normal points ofintersection between said outlines and said pitch circle at that end, anormal total-depth circle being maintained, in applying similar outlinecircles at the heel end, and causing them to pass through the normalpoints of intersection between the sides of said slot and the pitchcircle at that end, and in applying a total-depth circle, at the toeend, which has approximately the same relation to said second-namedoutline circles as does the-totaldepth circle, at the toe end, to saidfirst-named outline circles, wherefore the total-depth circle is deeperthan the normal total depth circle at the heel end.

4:. A"- method of laying out single-cut bevel gears consisting inestablishing the pitch circles and determining the generated outlines ofa tooth slot at the toe and heel ends, and establishing the total-depthcircle at the toe end, in approximating with circles the generatedoutlines at the toe end, said outline circles passing through the normalpoints of intersection between said outlines and the pitch circle atthat end, and in applying similar circles at the heel end in a manner tocause them to pass through the normal points of intersection betweensaid outlines and the pitch circle at that end, each of the centers ofsaid first-named outline circles being the same distance from the pointof intersection between the generated outline and the totaldepth circleon the same side with said center as is the companion center, at the toeend, and each of the centers of said second-named outline circles beingthe same distance from the point of intersection between the generatedoutline and the total-depth circle on the same side with said last-namedcenter as is the companion center, at the heel end. 5. A method oflaying out single-cut bevel ears consisting in developing a generatedtooth slot at the toe and heel ends, in approxi- .mating thegenerated-curve outlines at the toe end with circles which pass throughthe pitch circle at that end, the normal totaldepth circle beingmaintained, and in applying other outline circles at the heel end, andcausing them to pass through the normal points of intersection betweenthe sides of said slot and the pitch circle at that end, where thetotal-depth circle is deeper than the normal total-depth circle, thecutting angle being determined by a line extending between the actualtotal-depth circles.

6. A single-cut bevel gear each tooth of.

which is normal with a generated tooth on the pitch circles at has adedendum at the toe end which approximates in outline the generatedoutline, and a dedendum at the heel end which is similar to theapproximation ofthe dedendum at the toe end, but, being normal on thepitch line at that end,.extends deeper into the body of the gear thanwoulda generated form, with the result that the cutting angle of thesinglecut tooth is angular to the cutting angle of the generated tooth.

7 In a method of laying out single-cut bevel gears, the steps ofgenerating the outlines at the toe and heel ends of a developed toothslot, maintaining the total-depth circle at the toe end, finding atotal-depth circle at the heel end which is different from the normaltotal-depth circle atthat end, and connecting the actual total-depthcircles between the sidesoi. said slot with a straight line to determinethe cutting angle.

I-IIRAM D. CROFT.

the toe and heel ends, and

